1. Field of the Invention
This invention relates to an improvement in gas corrosion resistance, plasma resistance and corrosive solution resistance of vacuum chamber members and anodized Al parts used in the inside thereof, which are employed for the manufacturing process of semiconductor and liquid crystal device by a dry etching apparatus, a CVD apparatus, a PVD apparatus, an ion implantation apparatus, a sputtering apparatus or the like. More particularly, the invention relates to an improvement in corrosive solution resistance of Al alloy members that are exposed to a corrosive solution such as an acidic solution.
2. Description of Related Art
Because of the introduction of a corrosive gas including a halogen element, such as Cl, F, Br or the like, into the vacuum chamber used for the CVD apparatus, the PVD apparatus, the dry etching apparatus or the like as a reactant gas, an etching gas, a cleaning gas or the like, a corrosion resistance to a corrosive gas (hereinafter referred to as gas corrosion resistance) is required therefor. In the vacuum chamber, a halogen-based plasma is frequently generated in addition to the corrosive gas, so that importance is placed on a resistance to plasma (hereinafter referred to as plasma resistance). In recent years, the vacuum chamber of Al or Al alloys that are light in weight and excellent in thermal conductivity has been recently adopted for this purpose.
However, since Al or Al alloys do not have enough gas corrosion resistance and plasma resistance for the process conditions, a variety of surface-modifying techniques of improving these resistance characteristics have been proposed.
For improving the gas corrosion and plasma resistances, some techniques are proposed. For example, JP-B No. 53870/1993 shows that after formation of an anodic oxide film having a thickness of 0.5 to 20 xcexcm, heating and drying treatments are carried out in vacuum at 100 to 150xc2x0 C. to remove the moisture adsorbed in the film by evaporation. Further, JP-A No. 72098/1991 shows that an Al alloy containing 0.05 to 4.0% of copper is subjected to anodization treatment in an oxalic acid electrolytic solution, followed by dropping a voltage in the electrolytic solution.
The chamber members using these Al alloys, obtained by application of these techniques, exhibit excellent gas corrosion and plasma resistances. Nevertheless, when the chamber member is subjected to maintenance by wiping out by means of water or by washing with water, the halogen compound remained on the surface of the Al or Al alloy parts react with water to form an acidic solution. The chamber member does not have an enough resistance to corrosion with such an acidic solution (hereinafter referred to as acidic solution resistance), so that it has been experienced that corrosion of the anodized oxide film takes place therein. The CVD apparatus, PVD apparatus or dry etching apparatus has such members that while mounting a semiconductor wafer or liquid crystal glass substrate, the member is subjected to the cleaning step of the wafer or substrate. For the cleaning in the cleaning step, an acidic solution is used. The corrosion of the anodic oxide film could not be restrained, in fact, through the surface modification made according to the prior-art techniques. If an Al alloy vacuum chamber member, used in the manufacturing process of semiconductor or liquid crystal device, suffers corrosion, its electric characteristics locally change, thus impeding the uniformity of treatment during the course of the semiconductor/liquid crystal device manufacturing process. In this way, the known Al alloy members have never been fully responsible for these applications requiring excellent electric characteristics. For a technique solving these problems. JP Patent No. 2831488 discloses the technique wherein an anodic oxide film is subjected to fluorination treatment. Moreover, JP-A No. 207494/1995 discloses a technique of sealing pores in an anodic oxide film with a metal salt. In addition, JP-A No. 216589/1995 proposes a technique wherein after sealing the pores in an anodic oxide film, a silicon-based film is further formed thereover. Although the acidic solution resistance is improved to some extent according to these techniques, the resultant member does not have satisfactory resistances including all of the gas corrosion resistance, plasma resistance and acidic solution resistance, and thus, limitation is placed on the environment of its use. Additionally, the complicated treating procedures are necessary, so that high fabrication costs are inevitably invited, thus being devoid of general-purpose properties.
An object of the invention is to provide an Al alloy member which overcomes the problems of the prior-art techniques.
Another object of the invention is to provide an Al alloy member which are excellent in gas corrosion resistance, plasma resistance and acidic solution resistance.
The above objects can be achieved, according to the invention, by an Al alloy member which comprises an Al or Al alloy substrate and an anodic oxide film formed on the substrate and including a porous layer and a pore-free barrier layer wherein at least a part of a structure of the barrier layer is made of boehmite and/or pseudo-boehmite, a dissolution rate of the film, subjected to an immersion test in phosphoric acid/chromic acid (described in JIS H8683-2), is 100 mg/dm2/15 minutes or below, and a corroded area percent after allowing to be exposed to the condition of 5%Cl2xe2x80x94Ar gas at 400xc2x0 C. for 4 hours is 10% or below whereby the Al or Al member is excellent in corrosion resistances.
Preferably, the Al alloy should contain 0.1 to 2.0% (by weight herein and whenever it appears hereinafter) of Si, 0.1 to 3.5% of Mg, and 0.1 to 1.5% of Cu, or should contain 1.0 to 1.5% of Mn, 1.0 to 1.5% of Cu and 0.7 to 1.0% of Fe. The Al alloy member of the invention is conveniently used as a vacuum chamber member.
Other and further objects, features and advantages of the invention will appear more fully from the following description.